Electric lamp



July 16, 1957 M. WILDEBOER 2,799,421

ELECTRIC LAMP Filed A ril 22. 1954 INVEN-TOR MARINUS WILDEBOER United States Patent 2,799,421 ELECTRIC LAMP Application April 22, 1954, Serial No. 424,943 Claims priority, application Netherlands May 4, 1953 2 Claims. (Cl. 220-21) This invention relates to electric apparatus arranged in a glass envelope in which a hollow projection, a socalled head, is embraced by a cap cemented to the head. In such an apparatus the glass of the head is likely to crack at the point where the glass comes out of the cap, that is, at the edge of the cap. This defect is best known in electric filament lamps and is known as circular cracking.

It is an object of the invention to provide a construction which will substantially overcome this kind of cracking of the envelope.

The invention is based on the recognition of the fact that cracking is caused in the known constructions at the edge of the cap where the cap is arranged at the very point at which the envelope is comparatively weak, while the cap which embraces the glass up to its edge also brings about comparatively large stresses at this very point.

According to the invention the head is provided below the edge of the cap with a recessed groove and an adjacent thickened portion within the cap, the outer diameter of which portion is adapted to the inner diameter of the cap.

The term adapted is to be understood here to mean that the outer diameter of the thickened portion is arranged in the cap with such an amount of clearance that the cap can be moved over the head without difficulty, while that arrangement of the cap central to the head is properly ensured. The term recessed groove is to be understood to mean a groove which is not filled with cement; such cement might transmit the pressure of the cap to the glass. Small amounts of cement which do not fill the groove may be provided here. It is also possible to arrange a resilient mass, for example a sealing means, in the groove.

Due to this construction the transition stresses are set up in the thickened portion of the head only which is better capable of resisting such stresses.

Preferably the envelope is provided on the side of the recessed groove more remote from the cap with a wall portion transverse to the edge of the cap. Thus, correct arrangement of the cap is additionally ensured.

The invention will now be described with reference to the accompanying drawing, in which two embodiments are given by way of example, and in which:

Fig. 1 is partly an elevation, partly a sectional view of a glow lamp, and

Fig. 2 is a sectional view of a head and a cap of an alternative embodiment of such a lamp.

Referring to the drawing and more particularly to Fig. 1, a glow lamp comprising a glass envelope 1 is 2,799,421 Patented July 16, 1957 'ice a projection, the so-called head 2, to which a cap 3 is secured by means of a supply of cement 4-. Below the edge 5 of the cap 3 the head is provided with a recessed groove 6, and adjacent this groove within the cap with a thickened portion 7. The outer diameter of this thickened portion is slightly smaller than the inner diameter of the cap.

In order to arrange a cap on the head of an envelope usually a cement ring is arranged in the cap slightly spaced away from the edge 5. After the cap has been arranged on the head it is heated with the result that the cement flows and then hardens. The thickened portion 7 also prevents the cement from penetrating into the recessed groove 6. Consequently at this point no edge stresses can be transmitted to the head. Stresses will be exerted on the thickened portion 7, but this is strong enough to resist them.

The envelope 1 at the side of the recessed groove 6 more remote from the cap has a wall portion 8 transverse to the edge 5 of the cap. This portion supports the head when this is arranged on the head and ensures a correct placement of the cap on the head.

Fig. 2 shows an alternative embodiment of the head of a glass envelope which in this case may, for example, be used for a tubular lamp. Similarly to the case shown in Fig. 1 the recessed groove 6 is not filled with cement, but in this case a rubber ring 9 is arranged in the recessed groove, which ring provides a tight joint between the edge of the cap and the glass envelope.

It has been found that the construction according to the invention is particularly suitable for small filament lamps of a comparatively high output, such as motor car lamps.

While I have shown and described the preferred embodiment of my invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claims.

What is claimed is:

1. An electric lamp comprising a glass envelope having a hollow neck portion extending therefrom, a cap, cement means for securing said cap to said hollow neck portion, said neck portion being provided at its part covered by said cap with an annular projection having an outer diameter fitting within and abutting a portion of the inner diameter of said cap, said annular projection defining two zones of said neck portion above and below said annular projection being of smaller diameter than said annular projection and forming an area bounded by said cap and said neck portion, said cement means for securing the cap to the neck portion being only provided in that zone below said annular projection.

2. An electric lamp as set forth in claim 1, further comprising resilient sealing means arranged in said zone above said annular projection.

provided with References Cited in the file of this patent UNITED STATES PATENTS 530,895 Kaye Dec. 11, 1894 599,002 Lister Feb. 15, 1898 708,653 Miller Sept. 9, 1902 2,028,884 Thomas Ian. 28, 1936 

